Long-term trends in seagrass beds in the Mosquito Lagoon and northern Banana River, Florida

A long-term study of seagrass beds in lagoonal waters of Kennedy Space Center, Florida was conducted from 1983 to 1996 and included 8150 samples collected along 37 shallow water transects. Species composition and percent cover were determined at 5 m intervals along the transects using a canopy-coverage technique originally developed for terrestrial systems (Daubenmire 1968). Four seagrass species were found as well as one attached algae. The overall frequency of occurrence for each species indicated the following dominance: Halodule wrightii (71.9%), Ruppia maritima (23.7%), Syringodium filiforme (9.4%), Halophila engelmannii (2.3%), and Caulerpa prolifera (5.4%). Halodule wrightii and R. maritima were represented on most transects. S. filiforme was never encountered on 14 of 37 transects and, when it occurred, the most frequently recorded percent coverage was < 5%. Temporal trends in percent cover for Halodule wrightii indicate a significant long-term decline. R, maritima maintained an average occurrence of 26% and cover of 6% from 1983 to 1989. These averages dropped to 11% occurrence and 1.2% percent cover for 1990-1994. A marked increase occurred in 1995-1996 when occurrence was 49% and percent cover was 19%. The increase in R. maritima and declines in S. filiforme and Halodule wrightii appear to be linked to recent declines in salinity. An increase in the number of bare plots was also observed over the study. C. prolifera was observed in remarkably high coverages from 1986 to 1987, but rapidly declined by 1989. These data provide benchmarks that will be useful to researchers and managers in comparing trends observed elsewhere in the lagoon and determining if these are site-specific or regional trends.